Chemistry: electrical current producing apparatus – product – and – Means externally releasing internal gas pressure from closed...
Patent
1998-07-21
2000-05-16
Nuzzolillo, Maria
Chemistry: electrical current producing apparatus, product, and
Means externally releasing internal gas pressure from closed...
429 54, 429 56, 429 61, 429 62, H01M 212
Patent
active
060635185
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a sealed electrochemical cell fitted with a circuit-breaking terminal which ensures electrical connection between an external contact part of said terminal and one of the positive or negative electrodes of the cell, said external contact part of the terminal being electrically connected to a conductive wall which ensures that the terminal is sealed and which is capable of being deformed under the action of an increase in internal pressure, said wall being connected to said electrode by means which ensure electrical continuity, said electrical continuity being interrupted when an internal pressure P is reached which is greater than a determined value P.sub.1, causing said wall to deform and the connection between the wall and a break part to break.
U.S. Pat. No. 4,943,497 describes such a cell.
That device is particularly useful for Li-Ion storage cells. Such storage cells are generally constituted by: a positive electrode whose active material is a lithium-containing metal oxide, often selected from cobalt, nickel, and manganese oxides, and mixtures thereof; a negative electrode whose active material is a carbon-containing material selected from natural and artificial graphites, amorphous carbons and cokes, and mixtures thereof, which is capable of receiving lithium during charging; and a non-aqueous electrolyte. Such storage cells have the advantage of very high specific energy density, but the end-of-charge cuttoff voltage must be strictly controlled. When the limit is significantly exceeded, secondary reactions may occur following failure of the generally-associated protection and control circuits. Such reactions are generally associated with an increase in pressure and a rise in temperature, and it is advisable to be be able to interrupt the overcharging reaction early enough by interrupting the circuit.
The above-mentioned document therefore describes such an internal circuit-breaker which interrupts the charging current as soon as the internal pressure has increased in abnormal manner. Nevertheless, it is possible that pressure continues to rise and, in order to prevent an explosion, the above-mentioned prior art document provides that the deformable conductive wall, which ensures that the terminal is sealed, includes a weak point so that it breaks if the pressure continues to rise, thus enabling gas to escape outwards, thereby preventing the element from exploding.
Thus, the deformable wall therefore performs two distinct functions: 1) it ensures that the electrical circuit is interrupted in the event of a dangerous rise in pressure, and 2) it ensures that the gas escapes, thereby avoiding an explosion, were the pressure to continue to rise.
Two such functions are not desirable, since it is very difficult to ensure reliable operation of such a device, and there is a high risk that, during an increase in pressure, the wall, including a weak point will tear before reaching the pressure at which electrical disconnection would take place.
In addition, under such circumstances, pressure can no longer rise in the event of overcharging and electrical disconnection will not occur, thereby resulting in the risk of an explosion.
An object of the present invention is to propose a system which is much more reliable in operation, and which provides an electrochemical cell as defined above, said cell being characterized in that said circuit-breaking terminal passes in sealed manner through a closure lid of the cell, said lid also being fitted separately with a safety capsule which breaks under a pressure P.sub.2 >P.sub.1.
Thus, in the invention, the functions are clearly separated, and obtained by two quite distinct members, the deformable conductive wall which ensures that the terminal is sealed, has only one function, that of breaking the electrical connection between the wall and the electrode when it deforms under the effect of an increase in pressure. In addition, the capsule also has only one function, that of tearing under a pressure P.sub.2 >P.sub.1. Since the pressu
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Dewulf Frederic
Gerin Norbert
Nuzzolillo Maria
SAFT
Wills Monique
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